Here's the gist, though: Apple has built a complete, robust physics and particle engine for iOS 7. Elements don't just go from point A to point B, they move through a "real" world. They react to the accelerometer and gyroscope, they collide and bounce off each other and with the edges of the display, and they can change color according to the environment around them. They behave like objects in space, and interact like objects in a game.

Good piece by Rene Richie at iMore on how iOS 7 fundamentally changes the nature of UI design. Also worth looking at this ZDNet piece on iOS 7 Dynamic Type.